Economic-Related Inequalities in Zero-Dose Children: A Study of Non-Receipt of Diphtheria-Tetanus-Pertussis Immunization Using Household Health Survey Data from 89 Low- and Middle-Income Countries

Child immunization status according to number of siblings and birth order in 85 low- and middle-income countries: a cross-sectional study

Background

Identification of unvaccinated children is important for preventing deaths due to infections. Number of siblings and birth order have been postulated as risk factors for zero-dose prevalence.

Methods

We analysed nationally representative cross-sectional surveys from 85 low and middle-income countries (2010-2020) with information on immunisation status of children aged 12-35 months. Zero-dose prevalence was defined as the failure to receive any doses of DPT (diphtheria-pertussis-tetanus) vaccine. We examined associations with birth order and the number of siblings, adjusting for child's sex, maternal age and education, household wealth quintiles and place of residence. Poisson regression was used to calculate zero-dose prevalence ratios.

Findings

We studied 375,548 children, of whom 13.7% (n = 51,450) were classified as zero-dose. Prevalence increased monotonically with birth order and with the number of siblings, with prevalence increasing from 11.0% for firstborn children to 17.1% for birth order 5 or higher, and from 10.5% for children with no siblings to 17.2% for those with four or more siblings. Adjustment for confounders attenuated but did not eliminate these associations. The number of siblings remained as a strong risk factor when adjusted for confounders and birth order, but the reverse was not observed. Among children with the same number of siblings, there was no clear pattern in zero-dose prevalence by birth order; for instance, among children with two siblings, the prevalence was 13.0%, 14.7%, and 13.3% for firstborn, second, and third-born, respectively. Similar results were observed for girls and boys. 9513 families had two children aged 12-35 months. When the younger sibling was unvaccinated, 61.9% of the older siblings were also unvaccinated. On the other hand, when the younger sibling was vaccinated, only 5.9% of the older siblings were unvaccinated.

Interpretation

The number of siblings is a better predictor than birth order in identifying children to be targeted by immunization campaigns. Zero-dose children tend to be clustered within families.

Funding

Gavi, the Vaccine Alliance.

Measuring Zero-Dose Children: Reflections on Age Cohort Flexibilities for Targeted Immunization Surveys at the Local Level

Zero-dose (ZD) children is a critical objective in global health, and it is at the heart of the Immunization Agenda 2030 (IA2030) strategy. Coverage for the first dose of diphtheria-tetanus-pertussis (DTP1)-containing vaccine is the global operational indicator used to estimate ZD children. When surveys are used, DTP1 coverage estimates usually rely on information reported from caregivers of children aged 12-23 months. It is important to have a global definition of ZD children, but learning and operational needs at a country level may require different ZD measurement approaches. This article summarizes a recent workshop discussion on ZD measurement for targeted surveys at local levels related to flexibilities in age cohorts of inclusion from the ZD learning Hub (ZDLH) initiative-a learning initiative involving 5 consortia of 14 different organizations across 4 countries-Bangladesh, Mali, Nigeria, and Uganda-and a global learning partner. Those considerations may include the need to generate insights on immunization timeliness and on catch-up activities, made particularly relevant in the post-pandemic context; the need to compare results across different age cohort years to better identify systematically missed communities and validate programmatic priorities, and also generate insights on changes under dynamic contexts such as the introduction of a new ZD intervention or for recovering from the impact of health system shocks. Some practical considerations such as the potential need for a larger sample size when including comparisons across multiple cohort years but a potential reduction in the need for household visits to find eligible children, an increase in recall bias when older age groups are included and a reduction in recall bias for the first year of life, and a potential reduction in sample size needs and time needed to detect impact when the first year of life is included. Finally, the inclusion of the first year of life cohort in the survey may be particularly relevant and improve the utility of evidence for decision-making and enable its use in rapid learning cycles, as insights will be generated for the population being currently targeted by the program. For some of those reasons, the ZDLH initiative decided to align on a recommendation to include the age cohort from 18 weeks to 23 months, with enough power to enable disaggregation of key results across the two different cohort years. We argue that flexibilities with the age cohort for inclusion in targeted surveys at the local level may be an important principle to be considered. More research is needed to better understand in which contexts improvements in timeliness of DTP1 in the first year of life will translate to improvements in ZD results in the age cohort of 12-23 months as defined by the global DTP1 indicator.

Spatio-temporal analysis of childhood vaccine uptake in Nigeria: a hierarchical Bayesian Zero-inflated Poisson approach

BACKGROUND

Globally, child mortality and morbidity remain a serious health challenge and infectious diseases are the leading causes. The use of count models together with spatial analysis of the number of doses of childhood vaccines taken is limited in the literature. We used a Bayesian zero-inflated Poisson regression model with spatio-temporal components to assess the number of doses of childhood vaccines taken among children aged 12-23 months and their associated factors.

METHODS

Data of 19,564 children from 2003, 2008, 2013 and 2018 population-based cross-sectional Nigeria Demographic and Health Survey were used. The childhood vaccines include one dose of Bacillus-Calmette-Guérin; three doses of Diphtheria-Pertussis-Tetanus; three doses of Polio and one dose of Measles. Uptake of all nine vaccines was regarded as full vaccination. We examined the multilevel factors associated with the number of doses of childhood vaccines taken using descriptive, bivariable and multivariable Bayesian models. Analysis was conducted in Stata version 16 and R statistical packages, and visualization in ArcGIS.

RESULTS

The prevalence of full vaccination was 6.5% in 2003, 14.8% in 2008, 21.8% in 2013 and 23.3% in 2018. Full vaccination coverage ranged from 1.7% in Sokoto to 51.9% in Anambra. Factors associated with the number of doses of childhood vaccines taken include maternal age (adjusted Incidence "risk" Ratio (aIRR) = 1.05; 95% Credible Interval (CrI) = 1.03-1.07) for 25-34 years and (aIRR = 1.07; 95% CrI = 1.05-1.10) for 35-49 years and education: (aIRR = 1.11, 95% CrI = 1.09-1.14) for primary and (aIRR = 1.16; 95% CrI = 1.13-1.19) for secondary/tertiary education. Other significant factors are wealth status, antenatal care attendance, working status, use of skilled birth attendants, religion, mother's desire for the child, community poverty rate, community illiteracy, and community unemployment.

CONCLUSION

Although full vaccination has remained low, there have been improvements over the years with wide disparities across the states. Improving the uptake of vaccines by educating women on the benefits of hospital delivery and vaccines through radio jingles and posters should be embraced, and state-specific efforts should be made to address inequality in access to routine vaccination in Nigeria.

Estimating global and regional between-country inequality in routine childhood vaccine coverage in 195 countries and territories from 2019 to 2021: a longitudinal study

Background

Global routine childhood vaccine coverage has plateaued in recent years, and the COVID-19 pandemic further disrupted immunisation services. We estimated global and regional inequality of routine childhood vaccine coverage from 2019 to 2021, particularly assessing the impacts of the COVID-19 pandemic.

Methods

We used longitudinal data for 11 routine childhood vaccines from the WHO-UNICEF Estimates of National Immunization Coverage (WUENIC), including 195 countries and territories in 2019-2021. The slope index of inequality (SII) and relative index of inequality (RII) of each vaccine were calculated through linear regression to express the difference in coverage between the top and bottom 20% of countries at the global and regional levels. We also explored inequalities of routine childhood vaccine coverage by WHO regions and unvaccinated children by income groups.

Findings

Globally between January 1, 2019 and December 31, 2021, most childhood vaccines showed a declining trend in coverage, and therefore an increasing number of unvaccinated children, especially in low-income and lower-middle-income countries. Between-country inequalities existed for all 11 routine childhood vaccine coverage indicators. The SII for the third dose of diphtheria-tetanus-pertussis-containing vaccine (DTP3) coverage was 20.1 percentage points (95% confidence interval: 13.7, 26.5) in 2019, and rose to 23.6 (17.5, 30.0) in 2020 and 26.9 (20.0, 33.8) in 2021. Similar patterns were found for RII results and in other routine vaccines. In 2021, the second dose of measles-containing vaccine (MCV2) coverage had the highest global absolute inequality (31.2, [21.5-40.8]), and completed rotavirus vaccine (RotaC) coverage had the lowest (7.8, [-3.9, 19.5]). Among six WHO regions, the European Region consistently had the lowest inequalities, and the Western Pacific Region had the largest inequalities for many indicators, although both increased from 2019 to 2021.

Interpretation

Global and regional inequalities of routine childhood vaccine coverage persisted and substantially increased from 2019 to 2021. These findings reveal economic-related inequalities by vaccines, regions, and countries, and underscore the importance of reducing such inequalities. These inequalities were widened during the COVID-19 pandemic, resulting in even lower coverage and more unvaccinated children in low-income countries.

Funding

Bill & Melinda Gates Foundation.

Why Reaching Zero-Dose Children Holds the Key to Achieving the Sustainable Development Goals

Immunization has one of the highest coverage levels of any health intervention, yet there remain zero-dose children, defined as those who do not receive any routine immunizations. There were 18.2 million zero-dose children in 2021, and as they accounted for over 70% of all underimmunized children, reaching zero-dose children will be essential to meeting ambitious immunization coverage targets by 2030. While certain geographic locations, such as urban slum, remote rural, and conflict-affected settings, may place a child at higher risk of being zero-dose, zero-dose children are found in many places, and understanding the social, political, and economic barriers they face will be key to designing sustainable programs to reach them. This includes gender-related barriers to immunization and, in some countries, barriers related to ethnicity and religion, as well as the unique challenges associated with reaching nomadic, displaced, or migrant populations. Zero-dose children and their families face multiple deprivations related to wealth, education, water and sanitation, nutrition, and access to other health services, and they account for one-third of all child deaths in low- and middle-income countries. Reaching zero-dose children and missed communities is therefore critical to achieving the Sustainable Development Goals commitment to “leave no one behind”.

Inequalities in Immunization against Maternal and Neonatal Tetanus: A Cross-Sectional Analysis of Protection at Birth Coverage Using Household Health Survey Data from 76 Countries

Substantial progress in maternal and neonatal tetanus elimination has been made in the past 40 years, with dramatic reductions in neonatal tetanus incidence and mortality. However, twelve countries have still not achieved maternal and neonatal tetanus elimination, and many countries that have achieved elimination do not meet key sustainability thresholds to ensure long-lasting elimination. As maternal and neonatal tetanus is a vaccine-preventable disease (with coverage of the infant conferred by maternal immunization during and prior to pregnancy), maternal tetanus immunization coverage is a key metric for monitoring progress towards, equity in, and sustainability of tetanus elimination. In this study, we examine inequalities in tetanus protection at birth, a measure of maternal immunization coverage, across 76 countries and four dimensions of inequality via disaggregated data and summary measures of inequality. We find that substantial inequalities in coverage exist for wealth (with lower coverage among poorer wealth quintiles), maternal age (with lower coverage among younger mothers), maternal education (with lower coverage among less educated mothers), and place of residence (with lower coverage in rural areas). Inequalities existed for all dimensions across low- and lower-middle-income countries, and across maternal education and place of residence across upper-middle-income countries. Though global coverage changed little over the time period 2001-2020, this obscured substantial heterogeneity across countries. Notably, several countries had substantial increases in coverage accompanied by decreases in inequality, highlighting the need for equity considerations in maternal and neonatal tetanus elimination and sustainability efforts.

Assessing Potential Exemplars in Reducing Zero-Dose Children: A Novel Approach for Identifying Positive Outliers in Decreasing National Levels and Geographic Inequalities in Unvaccinated Children

Background: Understanding past successes in reaching unvaccinated or “zero-dose” children can help inform strategies for improving childhood immunization in other settings. Drawing from positive outlier methods, we developed a novel approach for identifying potential exemplars in reducing zero-dose children. Methods: Focusing on 2000–2019, we assessed changes in the percentage of under-one children with no doses of the diphtheria–tetanus–pertussis vaccine (no-DTP) across two geographic dimensions in 56 low- or lower-middle-income countries: (1) national levels; (2) subnational gaps, as defined as the difference between the 5th and 95th percentiles of no-DTP prevalence across second administrative units. Countries with the largest reductions for both metrics were considered positive outliers or potential ‘exemplars’, demonstrating exception progress in reducing national no-DTP prevalence and subnational inequalities. Last, so-called “neighborhood analyses” were conducted for the Gavi Learning Hub countries (Nigeria, Mali, Uganda, and Bangladesh), comparing them with countries that had similar no-DTP measures in 2000 but different trajectories through 2019. Results: From 2000 to 2019, the Democratic Republic of the Congo, Ethiopia, and India had the largest absolute decreases for the two no-DTP dimensions—national prevalence and subnational gaps—while Bangladesh and Burundi registered the largest relative reductions for each no-DTP metric. Neighborhood analyses highlighted possible opportunities for cross-country learning among Gavi Learning Hub countries and potential exemplars in reducing zero-dose children. Conclusions: Identifying where exceptional progress has occurred is the first step toward better understanding how such gains could be achieved elsewhere. Further examination of how countries have successfully reduced levels of zero-dose children—especially across variable contexts and different drivers of inequality—could support faster, sustainable advances toward greater vaccination equity worldwide.

Subnational Gender Inequality and Childhood Immunization: An Ecological Analysis of the Subnational Gender Development Index and DTP Coverage Outcomes across 57 Countries

The role of gender inequality in childhood immunization is an emerging area of focus for global efforts to improve immunization coverage and equity. Recent studies have examined the relationship between gender inequality and childhood immunization at national as well as individual levels; we hypothesize that the demonstrated relationship between greater gender equality and higher immunization coverage will also be evident when examining subnational-level data. We thus conducted an ecological analysis examining the association between the Subnational Gender Development Index (SGDI) and two measures of immunization-zero-dose diphtheria-tetanus-pertussis (DTP) prevalence and 3-dose DTP coverage. Using data from 2010-2019 across 702 subnational regions within 57 countries, we assessed these relationships using fractional logistic regression models, as well as a series of analyses to account for the nested geographies of subnational regions within countries. Subnational regions were dichotomized to higher gender inequality (top quintile of SGDI) and lower gender inequality (lower four quintiles of SGDI). In adjusted models, we find that subnational regions with higher gender inequality (favoring men) are expected to have 5.8 percentage points greater zero-dose prevalence than regions with lower inequality [16.4% (95% confidence interval (CI) 14.5-18.4%) in higher-inequality regions versus 10.6% (95% CI 9.5-11.7%) in lower-inequality regions], and 8.2 percentage points lower DTP3 immunization coverage [71.0% (95% CI 68.3-73.7%) in higher-inequality regions versus 79.2% (95% CI 77.7-80.7%) in lower-inequality regions]. In models accounting for country-level clustering of gender inequality, the magnitude and strength of associations are reduced somewhat, but remain statistically significant in the hypothesized direction. In conjunction with published work demonstrating meaningful associations between greater gender equality and better childhood immunization outcomes in individual- and country-level analyses, these findings lend further strength to calls for efforts towards greater gender equality to improve childhood immunization and child health outcomes broadly.

The Association between Childhood Immunization and Gender Inequality: A Multi-Country Ecological Analysis of Zero-Dose DTP Prevalence and DTP3 Immunization Coverage

This study explores the association between childhood immunization and gender inequality at the national level. Data for the study include annual country-level estimates of immunization among children aged 12–23 months, indicators of gender inequality, and associated factors for up to 165 countries from 2010–2019. The study examined the association between gender inequality, as measured by the gender development index and the gender inequality index, and two key outcomes: prevalence of children who received no doses of the DTP vaccine (zero-dose children) and children who received the third dose of the DTP vaccine (DTP3 coverage). Unadjusted and adjusted fractional logit regression models were used to identify the association between immunization and gender inequality. Gender inequality, as measured by the Gender Development Index, was positively and significantly associated with the proportion of zero-dose children (high inequality AOR = 1.61, 95% CI: 1.13–2.30). Consistently, full DTP3 immunization was negatively and significantly associated with gender inequality (high inequality AOR = 0.63, 95% CI: 0.46–0.86). These associations were robust to the use of an alternative gender inequality measure (the Gender Inequality Index) and were consistent across a range of model specifications controlling for demographic, economic, education, and health-related factors. Gender inequality at the national level is predictive of childhood immunization coverage, highlighting that addressing gender barriers is imperative to achieve universal coverage in immunization and to ensure that no child is left behind in routine vaccination.